Method for reducing chemical oxygen demand of wastewater from preparation of 2-ethylhexanol

Abstract

A method is disclosed for use in reducing chemical oxygen demand (COD) of alkaline wastewater generated from an aldol condensation reaction during a process for preparing 2-ethylhexanol, which teaches both high-boiling-point aldol mixtures and low-boiling-point aldol mixtures are used to serve as an extractant for reducing COD in the wastewater, and further to perform a stripping treatment, thereby a removal rate of COD in the wastewater of 89-93% is then achieved.

What is claimed is: 
     
         1 . A method for reducing chemical oxygen demand of wastewater from preparation of 2-ethylhexanol, comprising steps of:
 1) taking a high-boiling-point aldol mixture by-produced in the preparation of 2-ethylhexanol as a first extractant containing the following components with a total weight percent of 100%:
 a) an alcohol or an aldehyde having 4 carbon atoms, 0-5 wt %; 
 b) an alcohol or an aldehyde having 8 carbon atoms, 20-25 wt %; 
 c) an alcohol or an aldehyde having at least 9 carbon atoms, 70-80 wt %; and 
 d) water, 0-1 wt %; 
   2) taking a low-boiling-point aldol mixture by-produced in the preparation of 2-ethylhexanol as a second extractant containing the following components with a total weight percent of 100%:
 a) n-butanol, 60-70 wt %; 
 b) an alcohol or an aldehyde having 4 carbon atoms, 0-5 wt %; 
 c) an alcohol or an aldehyde having 8 carbon atoms, 10-20 wt %; 
 d) an alcohol or an aldehyde having at least 9 carbon atoms, 0-5wt %; and 
 e) water, 5-15wt %; 
   3) adding an inorganic acid to alkaline wastewaters produced from process for preparing of 2-ethylhexanol, to make the wastewater having a pH value of 0-4, wherein the inorganic acid is one or more selected from hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid;   4) extracting the wastewater acidized in Step 3) with the first extractant of Step 1), wherein a weight ratio of the first extractant to the wastewater ranges from 1:1 to 1:12;   5) extracting the acidized wastewater extracted in Step 4) with the second extractant of Step 2), wherein a weight ratio of the second extractant to the wastewater ranges from 1:1 to 1:45; and   6) introducing the acidified wastewater after extracted in Step 5) to a distillation column from top entering therein to meet a stripping medium entering the distillation column from bottom such that stripping happens at an operation temperature of 80-180° C. and a pressure of 0.5-4.5 kg/cm 2 , thereby achieving a removal rate of COD in the wastewater of 89-93%, wherein the stripping medium for the stripping is steam or an inert gas.   
     
     
         2 . The method for reducing chemical oxygen demand of wastewater as defined in  claim 1 , wherein the wastewater acidized in Step 3) has a pH value of 0-2. 
     
     
         3 . The method for reducing chemical oxygen demand of wastewater as defined in  claim 1 , wherein the weight ratio of the first extractant to the wastewater in Step 4) ranges from 1:1 to 1:6. 
     
     
         4 . The method for reducing chemical oxygen demand of wastewater as defined in  claim 1 , wherein the weight ratio of the second extractant to the wastewater in Step 5) ranges from 1:1 to 1:15. 
     
     
         5 . The method for reducing chemical oxygen demand of wastewater as defined in  claim 1 , wherein in step 6) uses nitrogen as the stripping medium for stripping. 
     
     
         6 . The method for reducing chemical oxygen demand of wastewater as defined in  claim 1 , wherein the stripping in step 6) is performed at an operation temperature ranging from 90° C. to 150° C. 
     
     
         7 . The method for reducing chemical oxygen demand of wastewater as defined in  claim 1 , wherein the stripping in step 6) is performed at an operation temperature ranging from 90° C. to 130° C. 
     
     
         8 . The method for reducing chemical oxygen demand of wastewater as defined in  claim 6 , wherein the stripping in step 6) is performed a pressure ranging from 0.5 kg/cm 2  to 2.75 kg/cm 2 . 
     
     
         9 . The method for reducing chemical oxygen demand of wastewater as defined in  claim 7 , wherein the stripping in step 6) is performed a pressure ranging from 1.0 kg/cm 2  to 2.4 kg/cm 2 .